1. Field of the Invention
This invention relates to a four-group zoom lens, and more particularly to improvements in a zoom lens in which a first group as a focusing portion having a positive refractive power, a second group as a magnification changing portion having a negative refractive power, a third group as a compensator portion having a positive refractive power, and a fourth group as a relay lens portion having a positive refractive power and the three groups adjacent to the object side form a substantially afocal system.
2. Description of the Prior Art
Nowadays, the performance of zoom lenses has been considerably improved, but there are not so many zoom lenses which are bright. Many of the conventional zoom lenses have been dark as compared with fixed focal length lenses and have been disadvantageous in focusing because viewfinder image is correspondingly dark. Also, when it has been necessary to effect photography with a high-speed shutter, the darkness of the zoom lenses has resulted in many inconveniences and it has often been the case that special shutter chances are lost. To overcome these problems, it is desired to provide zoom lenses with a great aperture ratio, but great aperture ratio zoom lenses are frequently used during opening and are therefore required to have a high performance even during full aperture.
Generally, as an optical system is made brighter, it becomes difficult to correct annular spherical aberration, coma and astigmatism and a number of lenses must be used for the correction of these aberrations, and this has necessarily led to a bulky and complicated construction.